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Amken USA edited this page Nov 19, 2025 · 1 revision

Endstop Implementation in Gopper

This document describes the endstop implementation in Gopper, which provides comprehensive support for various types of endstop sensors used in 3D printers.

Overview

Gopper implements Klipper-compatible endstop functionality with support for:

  • GPIO-based endstops (mechanical switches, hall effect sensors with digital output)
  • Analog endstops (ADC-based sensors, analog hall effect sensors)
  • I2C endstops (Time-of-Flight sensors like VL53L0X, VL53L1X, VL53L4CD)

Architecture

Core Components

  1. Trigger Synchronization (trsync) (core/trsync.go)

    • Coordinates multiple endstops during homing operations
    • Manages trigger callbacks and timeouts
    • Reports trigger events to the host

  2. GPIO Endstops (core/endstop.go)

    • Traditional mechanical switches
    • Hall effect sensors with digital output
    • Optical sensors with digital output
    • Uses timer-based sampling with oversampling to prevent false triggers

  3. Analog Endstops (core/endstop_analog.go)

    • Hall effect sensors with analog output
    • Pressure-sensitive sensors
    • Threshold-based triggering with hysteresis

  4. I2C Endstops (core/endstop_i2c.go)

    • Time-of-Flight (TOF) sensors (VL53L0X, VL53L1X, VL53L4CD)
    • Distance-based triggering with hysteresis

Command Protocol

Trigger Synchronization Commands

trsync_start

Format: trsync_start oid=%c report_clock=%u report_ticks=%u expire_reason=%c

Starts a trigger synchronization session for coordinated homing.

Parameters:

  • oid: Object ID of the trigger sync object
  • report_clock: Initial clock time for status reports
  • report_ticks: Interval between status reports (in timer ticks)
  • expire_reason: Reason code to report if timeout expires

trsync_set_timeout

Format: trsync_set_timeout oid=%c clock=%u

Sets a timeout for the trigger synchronization.

Parameters:

  • oid: Object ID of the trigger sync object
  • clock: Clock time when timeout expires

trsync_trigger

Format: trsync_trigger oid=%c reason=%c

Manually triggers a trsync object.

Parameters:

  • oid: Object ID of the trigger sync object
  • reason: Reason code for the trigger

Response: trsync_state

Format: trsync_state oid=%c can_trigger=%c trigger_reason=%c clock=%u

Reports the current state of a trigger sync object.

GPIO Endstop Commands

config_endstop

Format: config_endstop oid=%c pin=%u pull_up=%c

Configures a GPIO pin as an endstop input.

Parameters:

  • oid: Object ID for the endstop
  • pin: GPIO pin number
  • pull_up: 1 to enable pull-up resistor, 0 for pull-down

endstop_home

Format: endstop_home oid=%c clock=%u sample_ticks=%u sample_count=%c rest_ticks=%u pin_value=%c trsync_oid=%c trigger_reason=%c

Starts homing with a GPIO endstop.

Parameters:

  • oid: Object ID of the endstop
  • clock: Clock time to start checking
  • sample_ticks: Time between consecutive samples during oversampling
  • sample_count: Number of consecutive samples required to confirm trigger (0 to disable)
  • rest_ticks: Time between check cycles
  • pin_value: Expected pin value when triggered (1=high, 0=low)
  • trsync_oid: Object ID of the associated trigger sync
  • trigger_reason: Reason code to report when triggered

endstop_query_state

Format: endstop_query_state oid=%c

Queries the current state of an endstop.

Response: endstop_state

Format: endstop_state oid=%c homing=%c next_clock=%u pin_value=%c

Reports the current state of a GPIO endstop.

Analog Endstop Commands

config_analog_endstop

Format: config_analog_endstop oid=%c adc_oid=%c threshold=%u trigger_above=%c hysteresis=%u

Configures an analog (ADC-based) endstop.

Parameters:

  • oid: Object ID for the endstop
  • adc_oid: Object ID of the associated ADC channel
  • threshold: ADC value threshold for triggering
  • trigger_above: 1 to trigger when value > threshold, 0 when value < threshold
  • hysteresis: Hysteresis value to prevent oscillation

analog_endstop_home

Format: analog_endstop_home oid=%c clock=%u sample_ticks=%u sample_count=%c rest_ticks=%u trsync_oid=%c trigger_reason=%c

Starts homing with an analog endstop.

analog_endstop_query_state

Format: analog_endstop_query_state oid=%c

Queries the current state of an analog endstop.

Response: analog_endstop_state

Format: analog_endstop_state oid=%c homing=%c next_clock=%u value=%u

Reports the current state of an analog endstop, including the latest ADC value.

I2C Endstop Commands

config_i2c_endstop

Format: config_i2c_endstop oid=%c i2c_oid=%c addr=%c sensor_type=%c distance_threshold=%u trigger_below=%c hysteresis=%u

Configures an I2C-based endstop (e.g., TOF sensor).

Parameters:

  • oid: Object ID for the endstop
  • i2c_oid: Object ID of the associated I2C device
  • addr: I2C device address
  • sensor_type: Sensor type (0=VL53L0X, 1=VL53L1X, 2=VL53L4CD)
  • distance_threshold: Distance threshold for triggering (in mm)
  • trigger_below: 1 to trigger when distance < threshold, 0 when distance > threshold
  • hysteresis: Hysteresis value to prevent oscillation (in mm)

i2c_endstop_home

Format: i2c_endstop_home oid=%c clock=%u sample_ticks=%u sample_count=%c rest_ticks=%u trsync_oid=%c trigger_reason=%c

Starts homing with an I2C endstop.

i2c_endstop_query_state

Format: i2c_endstop_query_state oid=%c

Queries the current state of an I2C endstop.

Response: i2c_endstop_state

Format: i2c_endstop_state oid=%c homing=%c next_clock=%u distance=%u

Reports the current state of an I2C endstop, including the latest distance reading (in mm).

Implementation Details

Oversampling for Noise Rejection

All endstop types implement a two-stage detection mechanism to prevent false triggers:

  1. Initial Detection: The endstop is checked periodically (every rest_ticks)
  2. Oversampling: When a potential trigger is detected, the endstop is sampled multiple times consecutively (every sample_ticks) to confirm the trigger

This approach, borrowed from Klipper, prevents false triggers caused by electrical noise or mechanical bounce.

Trigger Synchronization

The trsync system coordinates multiple endstops during homing operations:

  1. Multiple endstops can be registered with the same trsync object
  2. When any endstop triggers, all registered callbacks are invoked
  3. The first trigger wins - subsequent triggers are ignored
  4. Timeout mechanism provides fallback if no endstop triggers

Platform Support

The endstop implementation is platform-agnostic and relies on HAL (Hardware Abstraction Layer) interfaces:

  • GPIO HAL: Provides pin configuration and reading
  • ADC HAL: Provides analog-to-digital conversion
  • I2C HAL: Provides I2C communication

Currently supported platforms:

  • RP2040 (Raspberry Pi Pico)
  • RP2350 (Raspberry Pi Pico 2)

Usage Examples

Basic Mechanical Switch

# Klipper configuration example
[stepper_x]
endstop_pin: ^gpio25  # Pull-up enabled

The firmware will:

  1. Configure GPIO25 as input with pull-up
  2. During homing, sample the pin multiple times to confirm trigger
  3. Report trigger to the host via trsync

Hall Effect Sensor (Analog)

# Klipper configuration example
[stepper_y]
endstop_pin: analog_endstop:ADC0

The firmware will:

  1. Configure ADC0 for analog sampling
  2. Monitor ADC value against threshold
  3. Use hysteresis to prevent oscillation
  4. Report trigger when threshold is crossed consistently

TOF Sensor (I2C)

# Klipper configuration example
[stepper_z]
endstop_pin: i2c_endstop:VL53L0X

The firmware will:

  1. Initialize VL53L0X sensor via I2C
  2. Periodically read distance measurements
  3. Trigger when distance crosses threshold
  4. Use hysteresis to prevent oscillation

Future Enhancements

Potential improvements for future releases:

  1. Sensorless Homing: Detect motor stall current for endstop detection
  2. Encoder-based Endstops: Use rotary encoders for position detection
  3. Multiple Sensor Fusion: Combine data from multiple sensor types
  4. Dynamic Threshold Adjustment: Auto-tune thresholds based on environmental conditions
  5. Advanced Filtering: Implement Kalman filtering for noisy sensors

References

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